1. Field of the Invention
The invention relates to a sulfur-vulcanizable rubber mixture without aromatic process oils, in particular for the tread rubber of vehicle pneumatic tires, containing at least one diene rubber, carbon black, mineral oil plasticizer, and resin. The invention also relates to a vehicle pneumatic tire with a tread rubber that is composed at least partially of a rubber mixture of this type vulcanized with sulfur.
2. Discussion of Background Information
Since the driving properties of a tire, in particular a vehicle pneumatic tire, are dependent to a large extent on the rubber composition of the tread rubber, particularly high demands are made on the composition of the tread rubber mixture. Thus various tests have been undertaken to affect the properties of the tire favorably by varying the polymer components, the fillers, and the other additives in the tread rubber mixture. It must be taken into consideration thereby that an improvement in the one tire property often entails a deterioration in another property. For tread rubber mixtures for automobile and van tires, for example, maximum demands are made with respect to the ABS dry braking and ABS wet braking, abrasion resistance, rolling resistance, handling, and durability.
Resins are additives for rubber mixtures for tire tread rubbers that have been known for a long time. They serve above all as processing aids and effect the necessary green tackiness of the rubber mixtures. Moreover, vulcanizate properties determined by the resins, such as hardness, modulus, and swelling behavior, can be affected. They can also be used as vulcanization resins or coupling agents. Adhesive resins typically used in the rubber industry are, e.g., coumarone-indene resins, petroleum resins, terpene resins, colophony resins, and phenol-formaldehyde resins.
It is known from EP-A 1 589 068, which is incorporated by reference herein in its entirety, for example, that for a higher flexibility with a simultaneously high stiffness, a rubber mixture for the tread rubber base contains cis-1,4-polyisoprene, polybutadiene with a high cis percentage, mineral oil plasticizers with a low content of polycyclic aromatic compounds, and carbon black, e.g., of the N121 type. The rubber mixture can also contain adhesive resins, which are not specified in more detail.
EP-B-0 899 297 and its family member U.S. Pat. No. 5,901,766, which are incorporated by reference herein in their entireties, disclose rubber mixtures for tire tread rubbers that are intended to provide an improved abrasion resistance and improvements in the traction and handling. The mixtures contain a rubber with a glass transition temperature of −80° C. to −110° C., another rubber with a higher glass transition temperature, carbon black, e.g., of the N220 type, aromatic plasticizer oil, and 15 to 50 phr of a resin. This resin can be for example coumarone-indene resins with an average molecular weight of 420 to 700 g/mol.
WO 02/072688 A1 and its family member U.S. Patent Publication No. 2004/0092644 A1, which are incorporated by reference herein in their entireties, also describe rubber mixtures that in addition to rubbers with different glass transition temperatures, aromatic plasticizer oils, and carbon black, also have resins with an average molecular weight of 400 to 2000 g/mol, e.g., coumarone-indene resins.
An important aspect in the area of durability is the chipping and chunking behavior of tread rubber mixtures. Chipping denotes thereby the flake-like detachment at the tire tread (thin peeling-off of rubber material) while driving over bad roads, while chunking denotes the breaking-out of large-volume pieces (e.g., tread lugs). The chipping and chunking behavior is further intensified by bad road conditions above all in countries with dry and hot climatic conditions—a critical tire property that is to be improved.